UltraLuxum CXL unveiled what is the currently largest trimaran in the world at the Monaco Yacht Show 2011, and I think the design might interest seasteading community as well:
Of course, this is a sailing trimaran, so it is designed for mobility in mind first, not for providing a stationary floating home.
However, the 48 meter long structure is quite interesting in its design, made entirely out of carbon fiber, making the body weight only 110 tons, rather light for a vessel of this size, lessening the fueling needs (together with the hybrid design with 55 meter long sails).
The living spaces on this previously concept design include 2 guest cabins with bathrooms, 1 owner’s cabin with bathroom, staff cabins apart from the living area, lounge area, dining area, gallery, navigation and technical center. I think the layout could provide clues as to how a seasteading barge could use its space most efficiently.
On the technical front, what is interesting is that the boat is highly flexible, with 2 sailing modes, using the extra side skirting on both sides, to operate with the hybrid diesel-electric engine powered with Lithium ion batteries. That modifiable spread-out could potentially provide design ideas for seasteading vehicles, changing the vessel from a seasteading unit to a fast-moving trimaran, if needed.